1. Field of the Invention
The present invention relates to a silicon seed crystal for use in the manufacture of a silicon single crystal by the Czochralski method and to a method for the production of a silicon single crystal by the use of the seed crystal.
2. Prior Art
In the production of a silicon single crystal by the Czochralski method, a silicon seed crystal is immersed in molten silicon and then grown until a desired diameter is attained. When the silicon seed crystal is immersed in the molten silicon, it generally generates a dislocation, or a crystal defect, with the immersed portion thereof as the center. The main reason for the generation of this dislocation is thought to be the thermal stress which is induced by a temperature difference occurring in the seed crystal before and after the immersion thereof into the melt. In the production of a silicon single crystal, it is indispensable to prevent the generation of dislocation or to remove the site of the generated dislocation. As a means to remove the dislocation which has occurred during the immersion, the dash necking process which provisionally decreases the diameter of the seed crystal after the immersion has previously been utilized. The largest decreased diameter that allows perfect elimination of the dislocation by the dash necking is about 4 mm. The dislocation cannot be perfectly eliminated when this diameter increases from this size.
Regarding the strength of the silicon for supporting the silicon single crystals which have acquired increased weights as a consequence of the trend in recent years toward silicon single crystals having increased diameters, the decreased diameter of 4 mm has the possibility of permitting the silicon to sustain a fracture. Thus, a method of producing the single crystal without requiring formation of a decreased diameter which poses a problem as to the strength of the silicon has been disclosed in the official gazette of JP-A-09-249,492. This prior art thus pertains to a technique which purports to increase the strength of a seed crystal by increasing the boron concentration in the seed crystal. It also inhibits the generation of a dislocation by the thermal stress occurring during the immersion of a silicon single crystal into the molten silicon or, when the dislocation is generated at all, it will repress the length thereof. It will enable the dislocation generated in a seed crystal to be eliminated by dissolving the seed crystal bar to an extent greater than the diameter of the seed crystal. It will allow the silicon single crystal to be grown without requiring formation of a part of a decreased diameter by necking.
The present inventors discovery performed in accordance with the procedure of the invention has shown that even when the seed crystal has such a high boron concentration as is proper for a conventional technique, the silicon crystal grown from this seed crystal occasionally generated a dislocation. That is, though the prior art indeed has succeeded in repressing significantly the generation of dislocation in the single crystal, it has failed to prevent perfectly the generation of a dislocation. It has also failed to elucidate clearly the quantitative causal relation between any factor other than the boron concentration and the generation of a dislocation.
It is therefore an object of the present invention to provide a seed crystal for the production of a silicon single crystal which is capable of preventing the significant generation of a dislocation which occurs when the seed crystal is immersed in the molten silicon during the production of a silicon single crystal by the Czochralski method. It is also capable of withstanding the load of a large weight of the silicon single crystal. The present invention has a further object which is to provide a method for the production of a silicon single crystal which permits the dislocation free ratio to be increased in the process for the production of a silicon single crystal by the Czochralski method.
Concerning the present invention, there is a concern about the state of a surface treatment given to a seed crystal. There is also a special interest in the amount of strain particularly on the surface of the seed crystal which have initiated a study on the effect of the state of surface treatment of the seed crystal on the significant generation of a dislocation during the growth of a silicon single crystal. This study has resulted in novel knowledge being introduced. This invention has been perfected as a result. Further, regarding this invention, a keen attention directed to the temperature fluctuation of the molten silicon has initiated a study on the effect of this temperature fluctuation on the significant generation of a dislocation in the seed crystal during the contacting of the seed crystal with the melt. This study has brought a novel knowledge. This invention has been also perfected as a result.
To be specific, the present invention includes providing the following items.
(1) A seed crystal for the production of a silicon single crystal for use in the manufacture of a silicon single crystal by the Czochralski method, wherein the boron concentration in the silicon single crystal as the matrix from which the silicon seed crystal is excised is not less than 4xc3x971018 atoms/cm3 and not more than 4xc3x971019 atoms/cm3 and the silicon seed crystal is excised from the silicon single crystal as the matrix, ground, and lapped, and subsequently subjected to surface etching, providing the amount to be etched of at least the part of the silicon seed crystal that is contiguous to the melt of silicon satisfies the following formula (I),
Formula I
Yxe2x89xa7exp(xe2x88x924.96xc3x97log A+18.7)xe2x80x83xe2x80x83(I)
wherein Y denotes the amount to be etched (xcexcm) and A denotes the size of particles (#) of a grindstone for the grinding specified in JIS (Japanese industrial standards) R 6001.
(2) A method for the production of a silicon single crystal by the Czochralski method, comprises using a seed crystal set forth in item (1) above and growing the crystal by pulling it without performing the dash necking process.
(3) A method for the production of a silicon single crystal by the Czochralski method, effected by using a seed crystal set forth in item (1) above and growing the crystal by pulling it without performing dash necking process and wherein the standard deviation of the temperature fluctuation of the melt of silicon in the time period of not less than 10 seconds is not more than 4xc2x0 C.
(4) A method for the production of a silicon single crystal by the Czochralski method, effected by using a seed crystal set forth in item (1) above, partially melting the seed crystal in the melt of silicon, and subsequently growing the silicon single crystal by pulling without performing the dash necking process and wherein the amount to be melted of the seed crystal is not less than the diameter of the seed crystal and the standard deviation of the temperature fluctuation of the melt of silicon in a time period of not less than 10 seconds is not more than 4xc2x0 C.